It is well known in the field that underground cables and pipelines are typically placed by laying the cable or pipeline in a prepared trench and subsequently back-filling the trench. Unfortunately, some cables and pipelines are susceptible to damage from stones or other hard objects in the backfill material. For example, optical fiber communications cables are considered particularly susceptible to damage in this manner, as are polymeric or plastic pipelines. Also, steel pipes are increasingly provided with protective polymeric coatings, which must be protected from penetration or damage by hard objects.
Consequently, in the laying of cables and pipelines, it is increasingly sought to back-fill the trench with fill material that is free of stones or other hard objects. One way to achieve this is to backfill the trench with sand or other suitable fill Material brought from a remote source of sand or rock-free soil. This approach is however relatively expensive and time consuming. Further, where steel pipe is covered with a layer of sand, the filled trench tends to collect sanding water in the porous sand fill, leading to premature corrosion of the pipe. Also, the use of a fill material that is different from the surrounding soil results in a loss of cathodic protection, which also leads to premature corrosion of steel pipe. The alternative is to screen the soil dug from the trench, remove stones and other foreign objects, and return the screened soil to the trench. Several machines, known as padding machines, have been disclosed within the prior art for this purpose.
For example, U.S. Pat. No. 2,857,691 To Curran discloses a tracked vehicle having a vertically swingable boom that extends laterally over a trench. The boom includes a tube having an enclosed auger. At the far end of the boom from the vehicle is a rotating head which scoops up soil from alongside the trench, screens the soil, and transmits it to the auger, which conveys the screened soil along the tube and into the trench through openings in the tube. The Curran apparatus is particularly designed for use with a vehicle that is driven along the opposite side of a trench from the pile of soil that was removed from the trench and which extends alongside the trench.
U.S. Pat. No. 4,633,602, to Layh, et al., teaches the use of a gathering belt that dumps material onto a separator screen, allowing fines to fall onto a lateral belt. This device does not provide for screening during the initial conveying nor is the device removably attachable to a vehicle, such as a hydraulic excavator, backhoe, or the like, as is the present invention.
Other examples are disclosed in U.S. Pat. Nos.: 3,596,384, 4,301,910 and 4,664,791. All of which are much too complicated and include many disadvantages which the present invention addresses and overcomes in a manner heretofore not seen nor taught within the prior art.
It is to be noted the padding machines that are currently available today are extremely large, and they are only primarily used for long-distance pipe laying operations in open country, where rights of way are wide and there is little or no rugged terrain. Such machines have limited usefulness where rights of way are narrow, where trenches do not follow a straight path, or where the terrain is relatively rugged.